Solid-state image sensing device manufacturing method and solid-state image sensing device

ABSTRACT

According to one embodiment, a solid-state image sensing device manufacturing method includes forming a photoelectric converting element, a diffusion layer included in a floating diffusion, and a read transistor, in a photoelectric converting element formation region of a semiconductor substrate, a floating diffusion formation region, and a read transistor formation region located between the photoelectric converting element formation region and the floating diffusion formation region, respectively, and forming a semiconductor layer including a impurity on the diffusion layer on the semiconductor substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This divisional application is based upon and claims the benefit ofpriority under 35 U.S.C. §120 from U.S. application Ser. No. 13/838,110,filed Mar. 15, 2013, which claims priority from prior Japanese PatentApplication No. 2012-202960, filed Sep. 14, 2012, the entire contents ofwhich are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a solid-state imagesensing device manufacturing method and a solid-state image sensingdevice.

BACKGROUND

Solid-state image sensing devices such as CCD image sensors and CMOSimage sensors are used for various purposes in, for example, digitalstill cameras, video cameras, or surveillance cameras. Single-plateimage sensors that acquire information for a plurality of colors by asingle pixel array are mainly used.

In recent years, back side illumination type image sensors that bring inlight from a subject from the back side of a semiconductor substratehave been under development.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the chip layout of asolid-state image sensing device according to an embodiment;

FIG. 2 is a diagram showing an example of the sectional structure of thesolid-state image sensing device according to the embodiment;

FIG. 3 is an equivalent circuit diagram of a pixel array and circuitslocated in its vicinity in the solid-state image sensing deviceaccording to the embodiment;

FIG. 4 is a plan view showing an example of the layout in the pixelarray of the solid-state image sensing device according to theembodiment;

FIG. 5 is a sectional view showing the structure of a cell included inthe solid-state image sensing device according to the embodiment;

FIG. 6 is a sectional process view showing a process in a method ofmanufacturing the solid-state image sensing device according to theembodiment;

FIG. 7 is a sectional process view showing a process in a method ofmanufacturing the solid-state image sensing device according to theembodiment;

FIG. 8 is a sectional process view showing a process in a method ofmanufacturing the solid-state image sensing device according to theembodiment;

FIG. 9 is a sectional process view showing a process in a method ofmanufacturing the solid-state image sensing device according to theembodiment;

FIG. 10 is a view showing modifications of the solid-state image sensingdevice according to the embodiment;

FIG. 11 is a view showing modifications of the solid-state image sensingdevice according to the embodiment;

FIG. 12 is a view showing modifications of the solid-state image sensingdevice according to the embodiment;

FIG. 13 is a view showing modifications of the solid-state image sensingdevice according to the embodiment; and

FIG. 14 is a view showing an application of the solid-state imagesensing device according to the embodiment.

DETAILED DESCRIPTION

[Embodiments]

Hereinafter, an embodiment will be described in detail with reference tothe drawings. Elements having the same functions and configurations areprovided with the same reference signs in the following explanation, andare repeatedly explained when necessary.

In general, according to one embodiment, a solid-state image sensingdevice manufacturing method includes forming a photoelectric convertingelement, a diffusion layer included in a floating diffusion, and a readtransistor, in a photoelectric converting element formation region of asemiconductor substrate, a floating diffusion formation region, and aread transistor formation region located between the photoelectricconverting element formation region and the floating diffusion formationregion, respectively; and forming a first semiconductor layer includinga first impurity on the diffusion layer on a first surface of thesemiconductor substrate.

(1) First Embodiment

A solid-state image sensing device and a solid-state image sensingdevice manufacturing method according to the first embodiment aredescribed with reference to FIG. 1 to FIG. 9.

(a) Structure

The structure of the solid-state image sensing device according to thefirst embodiment is described with reference to FIG. 1 to FIG. 5.

FIG. 1 is a schematic diagram showing a layout example of a chip of thesolid-state image sensing device (hereinafter referred to as an imagesensor) according to the present embodiment. FIG. 2 is a schematicsectional view showing the structure of the image sensor according tothe present embodiment.

As shown in FIG. 1 and FIG. 2, in an image sensor 100 according to thepresent embodiment, a pixel array 120 and a peripheral circuit region125 in which an analog circuit or logic circuit for controlling thepixel array 120 are formed is provided in one semiconductor substrate(chip) 150.

An Si single crystal substrate (bulk substrate) or an epitaxial layer ofan SOI substrate is used as the semiconductor substrate 150.

The pixel array 120 includes a plurality of unit cells UC. The unitcells (unit cell regions) UC are arranged in matrix form in the pixelarray 120.

Each unit cell UC includes a photoelectric converting element forconverting light from a subject (external light) to an electric signal.One unit cell UC includes at least one photoelectric converting element.A pixel is formed by using the photoelectric converting element. Aregion in which a pixel is formed inside the unit cell is called a pixelregion. Each pixel region includes one photoelectric converting element.

The unit cells UC adjacent to each other, the pixel regions adjacent toeach other, and photoelectric converting element adjacent to each otherare separated by a device isolation region 9. A formation region of eachunit cell UC or each photoelectric converting element is surrounded bythe device isolation region 9.

For example, a photodiode is used to form a photoelectric convertingelement 1. As shown in FIG. 2, the photodiode 1 is formed by at leastone impurity layer in the semiconductor substrate 150. The photodiode 1photoelectrically converts the light from the subject to an electricsignal (charge, voltage) corresponding to the amount of light. Thephotodiode 1 can store the generated charge in the impurity layer.

The unit cell UC includes a floating diffusion as a signal detector.

A diffusion layer (impurity semiconductor layer) 60 as a floatingdiffusion 6 is provided in the semiconductor substrate 150. Thediffusion layer 60 as the floating diffusion 6 temporarily holds acharge output from the photodiode 1 via a later-described field effecttransistor 2.

A semiconductor layer 61 is provided on the diffusion layer 60. Thesemiconductor layer 61 is used as the floating diffusion 6 together withthe diffusion layer 60. Hereinafter, the semiconductor layer 61 whichforms the floating diffusion 6 and which is provided on thesemiconductor substrate 150 will also be referred to as an elevatedfloating diffusion.

A read transistor 2 is provided on the semiconductor substrate 150between the photodiode 1 and the floating diffusion 6. A gate electrode20 of the read transistor 2 is provided on a channel region within thesemiconductor substrate 150 across a gate insulating film 21.

The unit cells UC (pixels) are used to form the image sensor 100. Theunit cell UC may include other components in addition to the at leastone photodiode 1, the floating diffusion 6, and the read transistor 2,in accordance with the circuit configuration of the image sensor 100.For example, the unit cell UC includes an amplifier transistor and areset transistor as the components.

As shown in FIG. 1 and FIG. 2, the peripheral circuit region 125 isprovided in the semiconductor substrate 150 to be adjacent to the pixelarray 120 across a device isolation region 9.

Circuits such as a later-described vertical shift register and an ADconversion circuit are provided in the peripheral circuit region 125.

The peripheral circuit region 125 is electrically isolated from thepixel array 120 by the device isolation region 9. For example, a deviceisolation insulating film 91 having an STI structure is embedded in thedevice isolation region 9 for dividing the peripheral circuit region125.

A plurality of devices such as a field effect transistor 7, a resistiveelement, and a capacitive element are used to form the circuits in theperipheral circuit region 125. In FIG. 2, the field effect transistor 7is only shown for simplicity. Although one field effect transistor isonly shown in FIG. 2, a plurality of devices to form peripheral circuitsare provided on the semiconductor substrate 150.

For example, in the peripheral circuit region 125, the field effecttransistor 7 is provided in a well region 159 within the semiconductorsubstrate 150. Two diffusion layers (impurity layers) 73 are provided inthe well region 159. The two diffusion layers 73 function as thesource/drain of the transistor 7. A gate electrode 70 is provided on thesurface of the well region (channel region) between the two diffusionlayers 73 via a gate insulating film 71. Thus, the field effecttransistor 7 is formed in the well region 159.

A plurality of interlayer insulating films 92 are stacked on thesemiconductor substrate 150 to cover the gate electrodes 20 and 70 ofthe transistors 2 and 7 and the upper surfaces of the photodiode 1. Forexample, silicon oxide is used for the interlayer insulating films 92.

A multilayer interconnection technique is used for the image sensor 100according to the present embodiment. That is, a plurality ofinterconnects 80 are provided in the stacked interlayer insulating films92 in accordance with each interconnect level (height based on thesurface of the substrate). By plugs 81, CP1, and CP2 that arerespectively embedded in the interlayer insulating films 92, theinterconnects 80 are electrically connected to other interconnectslocated at different interconnect levels. A dummy layer and a lightblocking film made of the same material as the interconnects 80 may beprovided in the interlayer insulating films 92.

The gate electrodes 20 and 70 of the transistors 2 and 7, thesource/drain diffusion layers 73, and terminals of the devices formed onthe semiconductor substrate 150 are connected to the interconnects 80 inthe interlayer insulating films 92 via the contact plugs CP1 and CP2.The lower interconnect 80 and the upper interconnect 80 connect thedevices provided on the semiconductor substrate 150 via the via plug 81embedded in the interlayer insulating films 92. Consequently, thecircuits in the image sensor 100 are formed by the multilayerinterconnection technique.

In the present embodiment, a surface in which devices are formed, morespecifically, the surface of the semiconductor substrate 150 in whichthe gate electrodes 20 and 70 of the transistors 2 and 7 are provided isreferred to as a front surface (first surface) of the semiconductorsubstrate 150. The interlayer insulating films 92 and the interconnects80 that are formed by the multilayer interconnection technique areprovided on the front surface of the semiconductor substrate 150.Hereinafter, the surface of the semiconductor substrate 150 opposite tothe front surface (the surface opposite to the front surface) in adirection perpendicular to the front surface of the semiconductorsubstrate 150 is referred to as a back surface (second surface, rearsurface). In the present embodiment, the front surface and back surfaceof the semiconductor substrate 150 are referred to as the main surfaceof the semiconductor substrate 150 when not distinguished from eachother.

A via (hereinafter referred to as a through via or a through electrode)88A is formed in the semiconductor substrate 150, for example, by athrough substrate via (TSV) technique to pass through the semiconductorsubstrate 150 from the front side of the semiconductor substrate 150 tothe back side (rear side). An insulating layer 98A is provided on theinner surface of the through-hole (opening) formed in the semiconductorsubstrate 150.

The through via 88A is connected to the interconnect 80 in theinterlayer insulating films 92 via the contact plug CP2. The through via88A is connected to a pad (electrode) 89 provided on the back side ofthe semiconductor substrate 150. The pad 89 is provided on an insulatinglayer (planarizing layer or protective layer) 97 on the back surface ofthe semiconductor substrate 150.

For example, in the present embodiment, a color filter 117 is providedon the back side of the semiconductor substrate 150 via a protectivelayer (not shown) and an adhesive layer (not shown), as shown in FIG. 2.

The color filter 117 is provided at a position corresponding to thepixel array 120 on the back side of the semiconductor substrate 150. Forexample, the image sensor 100 according to the present embodiment is asingle-plate image sensor. The color filter 117 used in the single-plateimage sensor has a plurality of dye films corresponding to a pluralityof colors (color information) included in the light from the subject.

The color filter 117 includes the dye films corresponding to red, blue,and green based on, for example, a bayer arrangement. One dye film isprovided to correspond to one photodiode (pixel) 1. The color filter 117may include white and yellow dye films in addition to the red, blue, andgreen.

A microlens array 118 is provided on the color filter 117 on the backside of the semiconductor substrate 150. The microlens array 118includes a plurality of microlenses corresponding to the respectivephotodiodes 1.

In the image sensor 100 according to the present embodiment, the colorfilter 117 and the microlens array 118 are provided on the surface (backsurface) of the semiconductor substrate 150 opposite to the surface(front surface) in which the gate electrodes 20 and 70 of thetransistors 2 and 7 and the interlayer insulating films 92 are provided.

The light from the subject is applied to the pixel array 120 from theback side of the semiconductor substrate 150 via the color filter 117,and brought into the photodiode 1.

A support substrate 119 is provided on the interlayer insulating film92. The support substrate 119 is stacked on the interlayer insulatingfilm 92, for example, via a protective layer (not shown) and an adhesivelayer (not shown). For example, a silicon substrate or an insulatingsubstrate is used for the support substrate 119. The semiconductorsubstrate 150 having the devices formed therein intervenes between thesupport substrate 119 and the color filter 117.

In the present embodiment, the surface to receive the light from thesubject is the back surface of the semiconductor substrate 150 to whichthe color filter 117 and the microlens array 118 are attached.

An image sensor, such as the image sensor 100 according to the presentembodiment, having a structure in which light from the back side of thesemiconductor substrate 150 is applied to the photodiode 1 is referredto as a back side illumination type image sensor.

An example of the circuit configuration of the pixel array 120 includedin the image sensor 100 according to the present embodiment is describedwith reference to FIG. 3.

FIG. 3 is a diagram showing a circuit configuration example of the pixelarray 120 and circuits in its vicinity.

As shown in FIG. 3, the unit cells UC are arranged in the pixel array120. Each unit cell UC is provided at the intersection of read controllines RD1 and RD2 and a vertical signal line VSL.

The unit cell shown in FIG. 3 has a two-pixel one-cell structure inwhich one unit cell UC includes two pixels. In the unit cell UC havingthe two-pixel one-cell structure, one floating diffusion 6 is shared bytwo photodiodes 1A and 1B.

The unit cell UC includes, for example, five transistors 2A, 2B, 3, 4,and 5. Each of the transistors 2A, 2B, 3, 4, and 5 is, for example, ann-channel MOS transistor. The transistors included in the unit cell UCare, for example, read transistors 2A and 2B, an amplifier transistor 5,an address transistor 4, and a reset transistor 3. In the unit cell UChaving the two-pixel one-cell structure, the two read transistors 2A and2B are provided to correspond to the photodiodes 1A and 1B,respectively.

The anodes of the photodiodes 1A and 1B are connected to a fixed voltageline, and are, for example, grounded (connected to a ground terminal).The cathodes of the photodiodes 1A and 1B are connected to the floatingdiffusion 6 via the current paths of the read transistors 2A and 2B,respectively. As described above, the photodiodes 1A and 1B convert thelight which has passed through the microlens and the color filter to anelectric signal (signal charge), and store the charge. Hereinafter, thephotodiodes 1A and 1B are referred to as the photodiode 1 when notdistinguished from each other.

Each of the read transistors 2A and 2B controls the storage and transferof the signal charge of each of the photodiodes 1A and 1B. The gates ofread transistor 2A and 2B are connected to the read control line RD1 andRD2, respectively. One ends of the current paths of the read transistors2A and 2B are connected to the cathode of the photodiode 1A and 1B,respectively. The other ends of the current paths of the readtransistors 2A and 2B are connected to the floating diffusion 6,respectively. Hereinafter, the read transistors 2A and 2B are referredto as the read transistor 2B when not distinguished from each other.

In the unit cell UC having the two-pixel one-cell structure, the resettransistor 3, the address transistor 4, and the amplifier transistor 5are shared by the two photodiodes 1A and 1B.

The reset transistor 3 resets the potential of the floating diffusion 6(the gate potential of the amplifier transistor 5). The gate of thereset transistor 3 is connected to a reset control line RST. One end ofthe current path of the reset transistor 3 is connected to the floatingdiffusion 6 and the other end of the current path of the resettransistor 3 is connected to a power supply terminal (for example,ground terminal).

The address transistor 4 functions as a selecting element to select(activate) the unit cell UC. The gate of the address transistor 4 isconnected to an address control line ADR. One end of the current path ofthe address transistor 4 is connected to the other end of the currentpath of the amplifier transistor 5 and the other end of the current pathof the address transistor 4 is connected to the power supply terminal(for example, ground terminal).

The amplifier transistor 5 amplifies a signal from the photodiode 1 heldby the floating diffusion 6. The gate of the amplifier transistor 5 isconnected to the floating diffusion 6. One end of the current path ofthe amplifier transistor 5 is connected to the vertical signal line VSLand the other end of the current path of the amplifier transistor 5 isconnected to one end of the current path of the address transistor 4.The signal amplified by the amplifier transistor 5 is output to thevertical signal line VSL as a signal of the unit cell (or pixel). Theamplifier transistor 5 functions as a source follower in the unit cellUC.

A vertical shift register 133 is connected to the two read control linesRD1 and RD2, an address control line ADR, and a reset control line RST.The vertical shift register 133 controls the potentials (signal levels)of the read control line RD1 and RD2, the address control line ADR, andthe reset control line RST to control and select a plurality of unitcells UC (and pixels) inside the pixel array 120 in rows. The verticalshift register 133 outputs a control signal (voltage pulse) to turntransistors 2A, 2B 3 and 4 on and off to control lines RD1, RD2, ADR andRST, respectively.

An AD conversion circuit 131 is connected to the vertical signal lineVSL. The AD conversion circuit 131 includes a processing unit PU toconvert an analog signal from the unit cell into a digital signal or toperform correlated double sampling (CDS) processing of a signal from theunit cell UC.

A load transistor 134 is used as a current source for the verticalsignal line VSL. One end of the current path of the load transistor 134is connected to one end of the current path of the amplifier transistor5 via the vertical signal line VSL. The other end of the current path ofthe load transistor 134 is connected to a power supply terminal (forexample, a grand terminal). The gate of the load transistor 134 isconnected to the other end of the current path of the load transistor134.

Each of the unit cells UC may include no address transistor 4. In thiscase, in the unit cell UC, the other end of the current path of theamplifier transistor 5 is connected to the other end of the current pathof the reset transistor 3 and a power supply terminal. When the unitcell UC includes no address transistor 4, the address control line ADRis not provided either.

The unit cell UC may have a one-pixel one-cell structure including onepixel. Alternatively, the unit cell UC may have a circuit configuration(multiple-pixel one-cell structure) in which one unit cell includesthree or more pixels (photodiodes) as in a four-pixel one-cell structureor an eight-pixel one-cell structure. In a unit cell including aplurality of pixels, three or more photodiodes share one floatingdiffusion, the reset transistor, the amplifier transistor, and theaddress transistor. In a unit cell including a plurality of pixels, oneread transistor is provided for each photodiode.

The structures of the pixel array and the unit cell of the image sensor100 according to the present embodiment are described with reference toFIG. 4 and FIG. 5.

FIG. 4 shows an example of the planar layout of the pixel array of theimage sensor 100 according to the present embodiment.

In FIG. 4, the layout of the unit cell UC having the two-pixel one-cellstructure in the pixel array 120 is shown.

As shown in FIG. 4, a region where the two photodiodes 1A and 1B areformed, and a region where the transistors 2, 3, 4, and 5 forcontrolling the operations of photodiodes and the floating diffusion 6are formed are provided in a formation region UA of the unit cell UC.

The region UA where the unit cell UC is formed is referred to as theunit cell formation region UA. Regions PAA and PAB where the photodiodesare formed are referred to as photodiode formation regions PAA and PAB.The photodiode formation regions PAA and PAB are referred to as thephotodiode formation region PA when not distinguished from each other.

A region where the read transistor is formed is referred to as a readtransistor formation region. A region where the floating diffusion 6 isformed is referred to as a floating diffusion formation region.

A region AA where the amplifier transistor 5, the reset transistor 3,and the address transistor 4 are formed is referred to as a transistorformation region (or active region) AA.

The unit cell formation region UA is divided by device isolation regions90 and 95 for each unit cell UC in the pixel array 120. The unit cellformation region UA is surrounded by the device isolation regions 90 and95.

The photodiode formation region PA, the read transistor formationregion, the floating diffusion formation region, and the transistorregion AA are semiconductor regions provided in the semiconductorsubstrate (chip) 150, in the unit cell formation region UA. In one unitcell formation region UA, at least the photodiode formation region, theread transistor formation region, and the floating diffusion formationregion are continuous semiconductor regions in the semiconductorsubstrate 150.

In one unit cell formation region UA, adjacent corners of the twophotodiode formation regions PAA and PAB are connected to one end of thelongitudinal direction (extending direction) of the rectangulartransistor formation region AA via the read transistor formation regionand the floating diffusion formation region.

The two photodiode formation regions PAA and PAB in one unit cellformation region UA are adjacent to each other in a y-direction acrossthe device isolation region (device isolation layer) 90. For example,the two photodiode formation regions PAA and PAB in one unit cellformation region UA are separated by an impurity semiconductor layer asthe device isolation layer 90.

However, the two pixel formation regions PAA and PAB in the unit cellformation region UA may be separated by the device isolation layer 90made of an insulator. That is, the pixel formation regions PA ofdifferent unit cell formation regions UA are electrically isolated bythe insulator as the device isolation layer.

The photodiode formation region PA includes impurity semiconductorlayers (diffusion layer, impurity semiconductor regions) 10A and 10B forforming the photodiode 1. For example, each of the impuritysemiconductor layers 10A and 10B in the photodiode formation region PAis used as one end (source/drain region) of the current path of the readtransistor 2.

In the read transistor formation region, the gate electrode 20 of theread transistor 2 is tilted relative to the extending direction of thetransistor formation region AA. In the two-pixel one-cell structure, theread transistors 2A and 2B respectively corresponding to the twophotodiodes 1A and 1B are switched on/off to electrically connect ordisconnect the photodiodes 1A and 1B and the floating diffusion 6provided in the continuous semiconductor regions.

The floating diffusion 6 is laid out in the unit cell formation regionUA to be surrounded by the gate electrodes 20 of the two readtransistors 2A and 2B and a gate electrode 30 of the reset transistor 3.The floating diffusion 6 is used as the other end (source/drain region)of the current path of the read transistor 2.

The transistor formation region is separated by an insulator as thedevice isolation layer 95. In the transistor formation region, the resettransistor 3, the amplifier transistor 5, and the address transistor 4are arranged in the extending direction of the transistor formationregion AA.

The gate electrode 30 of the reset transistor 3 is provided on thetransistor formation region AA via a gate insulating film. The channellength direction of the reset transistor 3 corresponds to the extendingdirection (longitudinal direction) of the transistor formation regionAA.

The floating diffusion 6 substantially serves as one end (source/drainregion) of the current path of the reset transistor 3. The other end ofthe current path of the reset transistor 3 is a diffusion layer(impurity semiconductor layer) provided in the transistor formationregion.

In the longitudinal direction of the transistor formation region AA, theaddress transistor 4 is located at the end opposite to the side (oneend) where the floating diffusion 6 is provided.

A gate electrode 40 of the address transistor 4 is provided on thetransistor formation region AA via a gate insulating film. Thesource/drain region as the other end of the current path of the addresstransistor 4 is provided at the end (opposite to the side where thefloating diffusion 6 is provided) of the extending direction of theactive region AA. The source/drain region as the other end of thecurrent path of the address transistor 4 is not shared with othertransistors. For example, a contact plug (not shown) is provided on thesource/drain region of the address transistor 4 which is not shared withother transistors.

In the transistor formation region AA, the amplifier transistor 5 islaid out between the reset transistor 3 and the address transistor 4.

Between the gate electrode 30 of the reset transistor 3 and the gateelectrode 40 of the address transistor 4, a gate electrode 50 of theamplifier transistor 5 is provided on the transistor formation region AAvia a gate insulating film.

A source/drain region as one end of the current path of the amplifiertransistor 5 is shared with the source/drain region as the other end ofthe current path of the reset transistor 3. The source/drain region asthe other end of the current path of the amplifier transistor 5 isshared with the source/drain region as one end of the current path ofthe address transistor 4.

The gate electrode 50 of the amplifier transistor 5 is connected to thefloating diffusion 6 via an interconnect and a plug.

In this way, the adjacent transistors 3, 4, and 5 share the source/drainregions (one end and the other of the current path). This allows thereduction of the area occupied by the unit cell formation region UA andthe miniaturization of the unit cell UC.

FIG. 5 shows a sectional structure along the line V-V of FIG. 4. In FIG.5, the photodiode 1, the read transistor 2, the floating diffusion 6,and the reset transistor 3 are shown as the components of the unit cellUC. The interconnects and the support substrate on the front side of thesemiconductor substrate 150, and the color filter and the microlensarray on the back side of the semiconductor substrate 150 are not shownin FIG. 5.

As shown in FIG. 5, the photodiode 1, the read transistor 2, thefloating diffusion 6, and the reset transistor 3 are provided in thecontinuous semiconductor regions.

When the photodiode 1 is formed in the P-type semiconductor substrate(semiconductor layer) 150, the photodiode 1 includes at least one N-typeimpurity semiconductor layer 10.

In FIG. 5, for the simplification of the drawing, one N-type impuritysemiconductor layer 10 is only shown as the component of the photodiode1. However, in order to improve the characteristics (e.g., sensitivityand photoelectric conversion efficiency) of the photodiode 1, aplurality of N-type and P-type impurity layers different in impurityconcentration in the depth direction of the semiconductor substrate 150may be provided in the photodiode formation region.

The gate electrode 20 of the read transistor 2 is provided on thesemiconductor substrate 150 via the gate insulating film 21. A sidewallinsulating film 29 is provided on the side surface of the gate electrode20.

In the semiconductor substrate 150, the semiconductor region between thetwo N-type impurity layers 10 and 60 serves as the channel of the readtransistor 2.

The gate electrode 30 of the reset transistor 3 in the transistorformation region is provided on the semiconductor substrate 150 via agate insulating film 31. The sidewall insulating film 29 is provided onthe side surface of the gate electrode 30. In the semiconductorsubstrate 150, the semiconductor region between the two N-type impuritylayers 60 and 35 serves as the channel of the reset transistor 3.

The amplifier transistor 5 and the address transistor 4 in thetransistor formation region also have substantially the same sectionalstructure as the reset transistor 3.

The floating diffusion 6 is provided in the semiconductor substrate 150to face the photodiode 1 across the read transistor 2. The photodiode 1and the floating diffusion 6 are arranged in the channel lengthdirection of the read transistor 2.

On the front side of the semiconductor substrate 150, a front surfaceshield layer 18 is provided in the N-type impurity layer 10 of thephotodiode 1. The front surface shield layer 18 is, for example, aP-type impurity layer. The front surface shield layer 18 is formed inthe surface layer of the N-type impurity semiconductor layer 10 at adistance from the channel region of the read transistor 2. The uppersurface of the front surface shield layer 18 contacts the interlayerinsulating films 92.

On the back side of the semiconductor substrate 150, a back surfaceshield layer 19 is provided in the semiconductor substrate 150. The backsurface shield layer 19 is, for example, a P-type impurity layer.

The front/back surface shield layers 18 and 19 can inhibit a darkcurrent generated in the photodiode 1.

In the present embodiment, the floating diffusion 6 is formed by thediffusion layer 60 and the semiconductor layer 61. In the floatingdiffusion formation region, the diffusion layer 60 is provided in thesemiconductor substrate 150, and the semiconductor layer 61 is providedon the diffusion layer 60 on the front side of the semiconductorsubstrate.

On the front side of the semiconductor substrate, the semiconductorlayer 61 as the elevated floating diffusion abuts on the diffusion layer60. A contact plug CPx is provided on the semiconductor layer 61. Aninterconnect 80 x is connected, via the contact plug CPx, to thediffusion layer 60 and the semiconductor layer 61 that form the floatingdiffusion 6.

The diffusion layer 60 as the floating diffusion is an N-typesemiconductor region forming at least one of phosphorus (P) and arsenic(As), and has an impurity concentration of, for example, about 1×10¹⁸cm⁻³. The diffusion layer 60 may have an impurity concentration of about1×10¹⁹ cm⁻³ to 1×10²⁰ cm⁻³.

The semiconductor layer 61 as the elevated floating diffusion containsan impurity. The semiconductor layer 61 includes one or more ofphosphorus, germanium (Ge), and carbon (C) as the impurity. For example,the semiconductor layer 61 is formed by a silicon layer to whichphosphorus is added, a silicon germanium (SiGe) layer, a silicon carbide(SiC) layer, or a silicon layer including germanium and carbon. The SiGelayer, the SiC layer, or the SiGeC layer may include phosphorus. Thesemiconductor layer may include boron (B) or As. The semiconductor layer61 may be a silicon layer (e.g., polysilicon) including no impurity.

Thus, the semiconductor layer 61 is preferably made of an n-type/p-typesilicon layer or mixed crystals including silicon as the main component.

The semiconductor layer 61 as the elevated floating diffusion is ahigh-concentration impurity semiconductor layer. The semiconductor layer61 has an impurity concentration (e.g., the concentration of phosphorus)of, for example, 1×10¹⁸ cm⁻³ to 1×10²⁰ cm⁻³.

For example, the impurity concentration in the semiconductor layer 61changes in a direction perpendicular to the main surface of thesemiconductor substrate. The impurity concentration on the bottom side(side that abuts on the semiconductor substrate) of the semiconductorlayer 61 is lower than the impurity concentration on the top side(interlayer insulating film side) of the semiconductor layer 61. Forexample, the impurity concentration in the bottom of the semiconductorlayer 61 in the vicinity of the interface between the semiconductorlayer 61 and the diffusion layer 60 is about 1×10¹⁸ cm⁻³.

For example, when the SiGe layer (or the SiC layer, the SiGC layer) isused as the semiconductor layer 61, the concentration of germanium (orcarbon, the total of germanium and carbon) on the bottom side of thesemiconductor layer 61 is about 5 at % (atomic %), and the concentrationof germanium on the top side of the semiconductor layer 61 is about 20at %.

The semiconductor layer 61 is, for example, an epitaxial layer. When thesemiconductor layer 61 is formed on the semiconductor substrate 150 byepitaxial growth, the semiconductor layer 61 has a sectional shapecorresponding to the crystal structure of the material used for thesemiconductor layer 61 and the crystal structure of the front surface ofthe semiconductor substrate 150 on which the semiconductor layer 61 isformed.

When the semiconductor layer 61 is an epitaxial layer which includes, asthe main component, silicon formed on the semiconductor substrate 150having a (100) face of Si on its front surface, the semiconductor layer61 has, for example, a trapezoidal sectional shape. The side surface ofthe semiconductor layer 61 including silicon as the main componentcorresponds to a (111) face of Si (or SiGe) and a face equivalentthereto. The top surface of the semiconductor layer 61 including siliconas the main component corresponds to the (100) face of Si (or SiGe) anda face equivalent thereto. The side surface of the semiconductor layer61 including silicon as the main component is tilted at an angle ofabout 55° degrees with the front surface of the semiconductor substrate.

The semiconductor layer 61 may be a polysilicon layer formed by a CVDmethod.

The semiconductor layer 61 as the elevated floating diffusion includes agettering site to trap a metal impurity (e.g., Fe) in the semiconductorsubstrate 150. The gettering site in the semiconductor layer 61 isformed by an added dopant or by crystal defects resulting from latticedistortion caused by the addition of the impurity.

The semiconductor layer 61 in the floating diffusion formation regionfunctions as the elevated floating diffusion, and also functions as thegettering site. The semiconductor layer 61 as the gettering layer 61includes a metal impurity (metal ions, metal element) such as Fe as wellas the added impurity.

Hereinafter, the semiconductor layer 61 may also be referred to as thegettering layer for the clarity of explanation.

For example, as in the shaded regions in FIG. 4, a semiconductor layer65 of the same material as the elevated floating diffusion 61 isprovided on the source/drain regions of the transistors 3, 4, and 5 inthe transistor formation region.

As shown in FIG. 5, in the transistor formation region AA, thesemiconductor layer 65 is provided on the source/drain diffusion layer35 of the transistors 3, 4, and 5, and abuts on the source/draindiffusion layer 35. The semiconductor layer 65 functions as thesource/drain of the transistors together with the diffusion layer 35. Acontact plug CPz is provided on the semiconductor layer 65, and connectsan interconnect 80 z and the source/drain region of the transistor 3.

The semiconductor layer 65 in the transistor formation region AAfunctions as a gettering layer in the same manner as the semiconductorlayer 61 in the floating diffusion formation region. Hereinafter, thesemiconductor layers 65 on the source/drain diffusion layers 35 of thetransistors 3, 4, and 5 may also be referred to as the gettering layers.

The gettering layers 61 and 65 are provided on the front surface of thesemiconductor substrate 150 to be adjacent to the gate electrodes 20 and30. The sidewall insulating film 29 is provided between the getteringlayers 61 and 65 and the gate electrodes 20 and 30. The sidewallinsulating film 29 is provided on the side surfaces of the gateelectrodes 20 and 30 to prevent direct contact between the getteringlayers 61 and 65 and the gate electrodes 20 and 30.

For example, the thickness of the gettering layers 61 and 65 is smallerthan the thickness of the gate electrodes 20 and 30 of the transistors 2and 3.

The space between the gettering layers 61 and 65 and the photodiodeformation region can be adjusted by the dimensions of the gate electrode20 of the read transistor 2 and the thickness of the sidewall insulatingfilm 29.

A layer made of the same material as the semiconductor layers 61 and 65may be provided on the source/drain diffusion layers 73 of thetransistor 7 in the peripheral circuit region 125 in FIG. 2. This layermay be used as a gettering layer in the peripheral region 125.

In the vicinity of the interface between the semiconductor layers(gettering layers) 61 and 65 and the diffusion layers 60 and 35 in thefloating diffusion formation region and the transistor formation region,a region (hereinafter referred to as a metal impurity region) 69 inwhich metal ions are segregated may be provided in the diffusion layers60 and 35. For example, the metal impurity concentration of thediffusion layers 60 and 35 in the floating diffusion formation regionand the transistor formation region is higher than the metal impurityconcentration in the channel region of the transistors 2 and 3 and inthe impurity layer 10 of the photodiode 1.

The diffusion layer 60 as the floating diffusion may include an impurity(e.g., Ge, or C) derived from the semiconductor layer 61.

A defect attributed to the metal impurity in the impurity semiconductorlayer 10 of the photodiode 1 behaves substantially in the same manner asa charge, and a defect caused by a recombination current resulting frommetal contamination emerges as a white defect (white spot) in an imageformed by the image sensor.

For example, in a manufacturing process of a general image sensor, themetal impurity in the semiconductor substrate is gettered by bulk microdefect (BMD) or polysilicon back seal (PBS).

As the BMD is formed in a region (region that abuts on the photodiodeformation region) immediately under the photodiode formation region, themetal impurity may remain in the impurity semiconductor layer of thephotodiode and in the regions located in its vicinity. Therefore, theBMD may lead to a risk of causing the white defect in the image sensor.

The PBS increases the heating temperature of the substrate for getteringto a relatively high temperature (600° C. or more) and applies the hightemperature to the substrate for a relatively long period so that themetal impurity will reach the back surface of the semiconductorsubstrate. The heat treatment for gettering by the PBS generates a heatload in the semiconductor substrate, the impurity region in thesemiconductor substrate, and the interconnect in the interlayerinsulating film, and the characteristics of the image sensor maydeteriorate.

When the floating diffusion including the diffusion layer is used as thegettering layer, the increase of the impurity concentration (e.g., 10²⁰cm⁻³) of the diffusion layer for gettering may increase the depth of thejunction between the diffusion layer and the semiconductor substrate andgenerate a leakage current.

In the image sensor according to the present embodiment, thesemiconductor layer 61 as the elevated floating diffusion is used as thegettering layer.

In a later-described manufacturing method, the semiconductor layer 61including a high-concentration impurity is formed on the front side ofthe semiconductor substrate 150 to abut on the diffusion layer 60, andthen the semiconductor substrate 150 is subjected to the heat treatmentfor gettering.

As a result of the heat treatment, a metal impurity such as Fe in thesemiconductor substrate 150 diffuses (moves) from the semiconductorsubstrate 150 into the semiconductor layer 61 as the gettering layer. Ametal impurity such as iron (Fe) ions in the impurity layer 10 of thephotodiode 1 is trapped in the semiconductor layer 61, and theconcentration of the metal impurity in the impurity layer 10 of thephotodiode 1 is reduced.

As in the present embodiment, the semiconductor layer 61 as the elevatedfloating diffusion and the gettering layer is provided in the regionrelatively close to the photodiode formation region, so thathigh-efficiency gettering can be performed by a heat treatment that doesnot generate an excessive heat load in the substrate, for example, aheat treatment within a relatively low temperature range (e.g., 300° C.to 600° C.)

The floating diffusion formation region in which the semiconductor layer61 as the gettering layer is provided is not directly adjacent to thephotodiode formation region. Therefore, the gettering layer locatedapart from the photodiode formation region can reduce that the metalimpurity which has been drawn to the gettering layer 61 located apartfrom the photodiode formation region remains in the photodiode formationregion (or its vicinity) after the gettering and can also inhibit theadverse effects of the remaining metal impurity, as compared with thecase in which the semiconductor layer 61 is provided in the regiondirectly adjacent to the photodiode formation region in a directionparallel to the front surface of the semiconductor substrate to abut onthe semiconductor substrate 150 or provided in the region thatvertically overlaps the photodiode formation region in a directionperpendicular to the front surface of the semiconductor substrate.

As described above, phosphorus having the function to trap the metalimpurity is added to the semiconductor layer. Thus, the metal impurityis more easily segregated (separated) in the semiconductor layer 61, andthe function of the semiconductor layer 61 as the gettering layer(gettering site) is improved.

When germanium or carbon is added to the silicon layer, latticedistortion (crystal defect) is generated in the layer as the getteringlayer. The gettering site is further formed in the silicon layer by thelattice distortion, and the efficiency of the gettering is improved.

According to the image sensor in the present embodiment, a highergettering efficiency can inhibit the increase of the heating temperaturefor gettering and inhibit the increase of the time for gettering. As aresult, the heat load applied to the components of the image sensor canbe reduced, and the deterioration of element characteristics caused byheat can be inhibited.

The use of the semiconductor layer as the elevated floating diffusion toa getting layer can reduce the impurity concentration of the diffusionlayer 60 as the floating diffusion. This can inhibit the increase of thejunction depth of the diffusion layer 60 and inhibit leakage currentgeneration.

In the present embodiment, the layer of the same material as thesemiconductor layer 61 serving as the elevated diffusion is formed onthe source/drain diffusion layer 35 of the transistors 2, 3, 4, and 5.The semiconductor layer 65 functioning as the gettering layer isprovided on the source/drain diffusion layer 35 of the transistors 2, 3,4, and 5, and the metal impurity in the channel region of thetransistors 2, 3, 4, and 5 is thereby trapped in the semiconductor layer65. As a result, the characteristic deterioration of the transistorresulting from the defect in the channel region is inhibited.

As described above, in the present embodiment, the defect caused by themetal impurity (e.g., Fe ions) remaining in the impurity layer 10 of thephotodiode 1 can be reduced by the relatively highly efficientgettering. As a result, the recombination current resulting from themetal impurity can be inhibited, and the generation of a white defect inan image formed by the image sensor can be inhibited.

Consequently, according to the image sensor in the present embodiment,the quality of the image formed by the image sensor can be improved.

The image sensor according to the embodiment has been described above asan example of the back side illumination type image sensor. However, theimage sensor according to the embodiment may be an image sensor whichbrings light from the subject from the front side of the semiconductorsubstrate (hereinafter referred to as a front side illumination typeimage sensor). Although the CMOS image sensor has been illustratedabove, the image sensor according to the embodiment may be a CCD imagesensor. The advantageous effects described above can be provided evenwhen the present embodiment is applied to the front side illuminationtype image sensor or the CCD image sensor.

(b) Manufacturing Method

A method of manufacturing the solid-state image sensing device (e.g.,image sensor) according to the first embodiment is described withreference to FIG. 6 to FIG. 9.

FIG. 6 to FIG. 9 show the sectional process views of a pixel array 120in the processes of the image sensor manufacturing method according tothe present embodiment. Here, FIG. 2, FIG. 4, and FIG. 5 are alsoproperly used in addition to FIG. 6 to FIG. 9 to describe the processesof the image sensor manufacturing method according to the presentembodiment.

In the method of manufacturing the image sensor according to the presentembodiment, the order of the formation of the components described latermay be properly changed as long as process consistency is ensured.

As shown in FIG. 2, a mask (not shown) formed by photolithography andreactive ion etching (RIE) is used to form a device isolation region anda device isolation layer 91 in a predetermined region (e.g., peripheralcircuit region) within a semiconductor substrate 150.

For example, as shown in FIG. 2, a device isolation trench having ashallow trench isolation (STI) structure is formed in the semiconductorsubstrate 150 in accordance with the mask. An insulator is embedded inthe device isolation trench by the chemical vapor deposition (CVD)method or a coating method. As a result, the device isolation layer 91having the STI structure is formed at a predetermined position in thesemiconductor substrate 150.

Thus, the pixel array 120, the unit cell regions in the pixel array 120,and the peripheral circuit region 125 are marked out in thesemiconductor substrate 150.

A mask different from the mask for forming the device isolation layer isused to form an N-type or P-type well region 159 in a predeterminedregion within the semiconductor substrate 150.

As shown in FIG. 5, components of unit cells (pixels) are formed in theunit cell regions of the pixel array 120. As shown in FIG. 2, components(e.g., transistors) of a peripheral circuit are formed in the wellregion 159 of the peripheral circuit region 125.

Gate insulating films 21 and 71 of transistors 2 and 7 are formed on theexposed surface (front surface) of the semiconductor substrate 150, forexample, by a thermal oxidation treatment of the semiconductor substrate150.

A polysilicon layer is deposited on the formed gate insulating films 21and 71 by the CVD method. The polysilicon layer is then fabricated byphotolithography and the RIE method, and gate electrodes 20 and 70having a predetermined gate length and a predetermined gate width areformed on the surface (first surface) of the semiconductor substrate 150across the gate insulating films 21 and 71.

As shown in FIG. 2 and FIG. 6, in the pixel array 120, the formed gateelectrode 22 and resist film (not shown) are used as masks, and theN-type impurity layer 10 of the photodiode 1 is formed in the photodiodeformation region within the unit cell formation region by an ionimplantation method.

In the floating diffusion formation region of the unit cell formationregion, a diffusion layer 60 as a floating diffusion 6 is formed in thesemiconductor substrate 150 by ion implantation so that the diffusionlayer 60 includes phosphorus having an impurity concentration of about10¹⁸ cm⁻³. The diffusion layer 60 may be formed to include ahigh-concentration (e.g., 10²⁰ cm⁻³ or more) impurity.

A diffusion layer 35 as the source/drain of each transistor, forexample, a reset transistor in the pixel array 120 is formed by ionimplantation so that the diffusion layer 35 has a predetermined impurityconcentration.

In the surface layer (exposed surface) of the N-type impuritysemiconductor layer 10 of the photodiode 1, a P-type impurity layer 18as the front surface shield layer 18 is formed in the N-type impuritysemiconductor layer 10 by ion implantation.

For example, the peripheral circuit region 125 is covered by a resistfilm (not shown) in a period in which ion implantation for forming thephotodiode 1 and the floating diffusion 6 are performed in the pixelarray 120.

When the diffusion layer (impurity semiconductor layer) is formed by ionimplantation, the crystallinity of the substrate may deteriorate.Therefore, annealing to recover the crystallinity of the substrate ispreferably performed between the ion implantation and the formation ofan epitaxial layer to allow for the formation of the epitaxial layer inthe subsequent process.

In the region (N-type or P-type well region) 159 in which the transistor7 is formed in the peripheral circuit region 125 shown in FIG. 2, aP-type or N-type impurity layer 73 as the source/drain of the transistor7 is formed in the semiconductor substrate 150 by ion implantation thatuses the gate electrode 70 as a mask. The process of forming thetransistor 7 in the peripheral circuit region 125 and the process offorming the transistor in the pixel array 120 may be a common process.

As shown in FIG. 7, sidewall insulating films 29 are formed in aself-aligning manner on the side surfaces of the gate electrodes 20 and30 of the read transistor 2 and the other transistors 3, 4, and 5.

After the sidewall insulating films 29 are formed on the side surfacesof the gate electrodes 20 and 30 of the transistors 2, 3, 4, and 5, asemiconductor layer 61 is formed, for example, by selective epitaxialgrowth on the diffusion layer 60 as the floating diffusion 6 on thefront side of the semiconductor substrate 150. At the same time, asemiconductor layer 65 is formed on the source/drain diffusion layer 35of the transistor.

The formed semiconductor layer 61 directly abuts on the diffusion layer60. When the semiconductor layer 61 is formed by selective epitaxialgrowth, the crystal of the semiconductor layer 61 is oriented dependingon the crystal face on the front surface of the semiconductor substrate,and the semiconductor layer 61 has a sectional shape corresponding tothe crystal orientation.

The semiconductor layers 61 and 65 are formed by semiconductor layersincluding, for example, silicon as the main component. The semiconductorlayer 61 formed in the floating diffusion formation region is used as anelevated floating diffusion and also used as a gettering layer. Thesemiconductor layer 65 provided in the transistor formation region isused as the source/drain and also used as a gettering layer.

For example, at least one impurity of germanium (Ge), phosphorus (P),and carbon (C) is added to the silicon layers 61 and 65 as the getteringlayers. For example, a doping gas is introduced during the deposition ofsilicon (hereinafter referred to as in-situ doping), and an impuritysuch as Ge, P, and C is thereby added to the silicon layers 61 and 65.The function of the semiconductor layer as the gettering site isimproved by the addition of the impurity to the silicon layers 61 and65.

For example, an impurity (e.g., phosphorus) is added so that theconcentration of the N-type (or P-type) dopant in the semiconductorlayers 61 and 65 will be 1×10¹⁸ cm⁻³ to 1×10²⁰ cm⁻³. In this case, thesemiconductor layer 61 has a concentration profile that varies in adirection perpendicular to the front surface of the semiconductorsubstrate, and the impurity concentration on the bottom side (side thatabuts on the diffusion layer 60) of the semiconductor layer 61 is lowerthan the impurity concentration on the top side of the semiconductorsubstrate. When the semiconductor layers 61 and 65 are silicon layers,the metal impurity is more easily segregated in the silicon layers 61and 65 during gettering by the addition of the P-type or N-type dopantin the silicon layers.

Ge or C added to the silicon layers is lattice-substituted for the Sielement in the silicon layers, and a mixed crystal layer of SiGe or SiCor SiGeC is formed. The concentration of Ge or C in the silicon layersis about 5 at % to 20 at %. Ge and C also have a concentration profilethat varies in a direction perpendicular to the front surface of thesemiconductor substrate, and the concentration on the bottom sides ofthe semiconductor layers 61 and 65 is lower than the concentration onthe top side of the semiconductor layer. Lattice distortion (latticedefect) resulting from lattice mismatch between the semiconductorsubstrate and the epitaxial layers 61 and 65 is caused by the additionof at least one of Ge and C to the silicon layer. The function of thesemiconductor layers 61 and 65 as the gettering sites is improved by thelattice defect.

Ge or C resulting from the semiconductor layer 61 may diffuse in thediffusion layer 60 within the floating diffusion formation region. Thesemiconductor layers 61 and 65 may be formed by the CVD method.

For example, an insulating film (not shown) is formed in advance on theimpurity semiconductor layer 10 of the photodiode and the front surfaceshield layer 18 so that a semiconductor layer that directly abuts on thesemiconductor substrate 150 may not be formed in the photodiodeformation region during the formation of the semiconductor layers 61 and65 as the gettering layers by the selective epitaxial growth.Alternatively, after the formation of a semiconductor layer, thesemiconductor layer is selectively removed from the photodiode formationregion.

As shown in FIG. 8, the semiconductor substrate 150 is subjected to, forexample, a heat treatment of about 600° C. and the subsequent heattreatment in a temperature range of about 300° C. to 500° C. forgettering while the semiconductor layers 61 and 65 are provided on thefront surface of the semiconductor substrate 150. The heat treatment forgettering may be conducted by the two-stage heat treatments different inthe temperature range, or may be conducted by a heat treatment in whichthe temperature is slowly dropped from, for example, about 600° C. toabout 300° C. (a heat treatment having a gentle temperature changegradient).

Thus, a metal impurity 200 in the semiconductor substrate 150 diffuses(moves) into the gettering layers 61 and 65 or into the diffusion layers60 and 35 that abut on the gettering layers 61 and 65, and the metalimpurity 200 is trapped in the gettering layers 61 and 65.

As a result, the metal impurity 200, for example, Fe moves to thefloating diffusion formation region from the impurity semiconductorlayer 10 in the photodiode formation region and its vicinity, and theconcentration of the metal impurity in the impurity semiconductor layer10 within the photodiode formation region decreases or substantiallyreaches zero. The concentration of the metal impurity in the floatingdiffusion formation region is higher than the concentration of the metalimpurity in the photodiode formation region.

The metal impurity 200 in the channel region of the transistor istrapped in the gettering layer 65 on the source/drain diffusion layer35.

When the gettering is conducted, a metal impurity region 69 may beformed in the vicinity of the interface between the semiconductor layers61 and 65 as the gettering layers and the diffusion layer 60.

Thus, a metal impurity such as Fe is removed from the impuritysemiconductor layer 10 within the photodiode formation region and itsneighboring regions by the gettering treatment that uses thesemiconductor layer 61 as the gettering layer (gettering site) formed inthe floating diffusion formation region.

As shown in FIG. 9, after the metal impurity is removed from thephotodiode formation region by the gettering, the gettering layers 61and 65 are selectively etched. As a result, most of the gettering layers61 and 65 are removed.

For example, as shown in FIG. 9, the thin gettering layers 61 and 65 mayremain on the diffusion layers 60 and 35. For example, high impurityconcentration regions in the gettering layers 61 and 65 are removed, lowimpurity concentration regions (e.g., region including an impurity ofabout 1×10¹⁸ cm⁻³) remain on the diffusion layers 60 and 35.

Thus, most of the gettering layers are removed after the gettering, sothat it is possible to prevent the metal impurity trapped in thesemiconductor layers 61 and 65 as the gettering layers from beingre-diffused into the semiconductor substrate 150 by the heat treatmentafter the gettering in the manufacturing process of the image sensor100.

As shown in FIG. 2 and FIG. 5, a multilayer interconnection structureincluding a plurality of interlayer insulating films 92 and a pluralityof interconnects 80 is formed by the multilayer interconnectiontechnique on the front surface of the semiconductor substrate 150 onwhich the gate electrode 20 of the transistor 2 is formed. Theinterlayer insulating films 92 cover the front surface of thesemiconductor substrate 150, and cover, for example, the gate electrode20 of the transistor 2.

In the formation process of the multilayer interconnection structure ateach interconnect level, for example, the interlayer insulating film 92which is a silicon oxide film is deposited by the CVD method. At eachinterconnect level, the interlayer insulating film 92 is planarized by aCMP method, and a contact plug CP1 and a via plug 81 are embedded in acontact hole formed in the interlayer insulating film 92 byphotolithography and the RIE method.

A contact plug CPx is embedded in the interlayer insulating film 92 sothat the contact plug CPx is connected to the semiconductor layer 61remaining in the floating diffusion formation region. Thus, thesemiconductor layer 61 used as the gettering layer 61 is reused as anelevated floating diffusion.

A contact plug CPz is also embedded in the interlayer insulating film 92so that the contact plug CPz is connected to the semiconductor layer 65remaining in the transistor formation region. Thus, the semiconductorlayer 61 used as the gettering layer 61 is reused as the source/drain ofthe transistor.

For example, a conductive layer of aluminum is deposited on theinterlayer insulating film 92 and on the plugs CP1, CPx, CPz, and 81 bya sputter method. The deposited conductive layer is fabricated into apredetermined shape by photolithography and the RIE method so that theconductive layer is connected to the plugs CP1, CPx, CPz, and 81. As aresult, conductive layers 80, 80 x, and 80 z as interconnects areformed. The interconnects 80, 80 x, and 80 z made of copper or a copperalloy may be formed in a self-aligning manner by a damascene method in atrench (damascene trench) formed in the interlayer insulating film.

Thus, a plurality of elements 1, 2, and 7 of the semiconductor substrate150 are connected by the interconnects of the multilayer interconnectiontechnique, and each circuit of the image sensor is formed.

When a back side illumination type image sensor is formed, the uppermostinterlayer insulating film 92 (and the conductive layer) on the frontside of the semiconductor substrate 150 is planarized as shown in FIG. 2and FIG. 5, and an adhesive layer (not shown) is then formed on theplanarized surface of the uppermost interlayer insulating film 92. Asupport substrate 119 is then attached to the adhesive layer on theinterlayer insulating film 92. Thus, the support substrate 119 is bondedto the interlayer insulating film 92 covering the front surface of thesemiconductor substrate.

For example, before the support substrate 119 is attached to theinterlayer insulating film 92, a redistribution layer may be formed by aredistribution technique on the uppermost interlayer insulating film 92so that the redistribution layer is connected to the interconnect in theinterlayer insulating film 92.

After the support substrate 119 is attached to the interlayer insulatingfilm 92, the back surface of the semiconductor substrate 150 isselectively etched, for example, by the CMP method and by wet etchingthat uses an HF solution. As a result, the semiconductor substrate 150is reduced in thickness.

As shown in FIG. 2 and FIG. 5, after the semiconductor substrate 150 isreduced in thickness, a P-type impurity semiconductor layer 19 as a backsurface shield layer 19 is formed in the semiconductor substrate 150within the pixel array 120 by ion implantation on the back surface ofthe semiconductor substrate 150.

After a protective film 97 is formed on the back surface of thesemiconductor substrate, a color filter 117 is formed on the protectivefilm 97 located at a position corresponding to the pixel array 120.

An insulating film (not shown) as a protective film is formed on theformed color filter 117. A microlens array 118 is formed on theprotective film covering the color filter 117.

Before or after the formation of the color filter 117 and the microlensarray 118, an interconnect, pad, or metal light blocking film on theback side of the semiconductor substrate 150 may be formed.

For example, after the formation of the color filter 117 and themicrolens array 118, a through via 88A is embedded in a through-holeformed in the semiconductor substrate 150, as shown in FIG. 2. Thethrough via 88A may be formed before the formation of the color filter117 and the microlens array 118.

The image sensor according to the present embodiment is formed by theprocess described above.

On the front side of the semiconductor substrate in the floatingdiffusion formation region, the semiconductor layers 61 and 65 as thegettering layers are formed on the semiconductor substrate 150. Thegettering layers 61 and 65 are formed to abut on the upper surface ofthe diffusion layer 60 as a floating diffusion FD.

As a result of gettering, the metal impurity (e.g., Fe) in thephotodiode formation region is trapped in the gettering layers 61 and 65by the action of high-concentration phosphorus added to the getteringlayers 61 and 65 and by the action of the lattice defect resulting fromGe or C added to the gettering layers (layers including silicon as themain component).

As in the present embodiment, the gettering layer 61 is formed in theregion relatively close to the photodiode formation region, so that theefficiency of the gettering is increased, and the concentration of themetal impurity in the impurity semiconductor layer 10 in the photodiodeformation region and its vicinity is reduced. Moreover, according to thepresent embodiment, the gettering layer 61 is formed in the region thatdoes not directly abut on the photodiode formation region. Therefore, itcan be reduced that the metal impurity drawn to the gettering layer 61remains in the photodiode formation region and its vicinity, and theadverse effects of the metal impurity on the characteristics of thephotodiode can be inhibited.

Thus, in the image sensor manufacturing method according to the presentembodiment, the gettering layers are formed in the vicinity of thephotodiode formation region, so that the adverse effects of theremaining metal impurity can be inhibited, and the gettering can berelatively efficiently performed.

Consequently, according to the present embodiment, the increase of theheating temperature for gettering can be inhibited, and the increase ofthe time for gettering can be inhibited. As a result, according to theimage sensor manufacturing method of the present embodiment, the heatload applied to the components of the image sensor can be reduced. Thus,according to the present embodiment, it is possible to inhibit thedeterioration of the elements included in the image sensor caused byheat; for example, the deterioration of the interconnects/insulatingfilms and unintended diffusion (dispersion) of the impurity (or dopant)caused by heat.

In the transistor formation region, the metal impurity in the channelregion of the transistor is trapped in the gettering layer 65 formed inthe source/drain region. As a result, the metal impurity in the channelregion is reduced, and a transistor of improved characteristics isformed.

Known gettering techniques such as the BMD and the PBS may be usedtogether with the gettering that uses the semiconductor layer providedin the floating diffusion formation region.

As described above, according to the solid-state image sensing deviceand the manufacturing method of the same in the first embodiment, it ispossible to provide an image sensor that can improve the image quality.

(2) Modifications

Modifications of the solid-state image sensing device according to theembodiment are described with reference to FIG. 10 to FIG. 13.

In the modifications, the components which are substantially the same asthose in the first embodiment are described when necessary. In FIG. 10to FIG. 13, the interlayer insulating film and the color filter aresimplified or not shown, as in the embodiment described above.

EXAMPLE 1

The modification of the image sensor manufacturing method according tothe embodiment is described with reference to FIG. 10.

FIG. 10 is a sectional process view illustrating the modification of theimage sensor manufacturing method according to the embodiment.

In the image sensor manufacturing method according to the embodimentdescribed with reference to FIG. 5 to FIG. 9, the gettering layers 61and 65 to which an impurity is added are formed by enclosing a gasincluding P or Ge together with an Si formation gas during thedeposition of the silicon layer (Si layer that includes at least one ofP, Ge, and C) in the process of forming the semiconductor layers 61 and65 as the gettering layers.

However, the impurity in the gettering layers 61 and 65 may be added byion implantation to the gettering layers 61 and 65 deposited on thesemiconductor substrate 150.

As shown in FIG. 10, a non-doped Si layer (or SiGe layer) 61Z is formed,for example, by the selective epitaxial growth on the semiconductorsubstrate 150 in the floating diffusion formation region and thetransistor formation region.

The semiconductor substrate 150 is coated with a resist film. An openingis formed in the resist film by lithography and RIE so that the Si layer61Z is exposed, and a mask layer 209 is formed.

Ion implantation is conducted while the mask layer 209 is formed on thesemiconductor substrate 150. At least one of P, Ge, and C is added tothe non-doped Si layer 61Z by ion implantation. As a result, a getteringlayer 61Z including a gettering site is formed.

After the mask layer 209 is removed, gettering is performed as shown inFIG. 8, and the metal impurity in the semiconductor substrate 150 istrapped in the gettering layer 61Z.

The manufacturing processes described with reference to FIG. 9, FIG. 2,and FIG. 5 are then sequentially carried out, and the image sensoraccording to the present embodiment is formed.

EXAMPLE 2

The modification of the image sensor and the manufacturing method of thesame according to the embodiment are described with reference to FIG.11.

FIG. 11 is a sectional process view illustrating the modification of theimage sensor manufacturing method according to the embodiment.

As shown in FIG. 11, the gettering layer may be removed from thesemiconductor substrate 150 after gettering.

When the gettering layer is removed, the contact plug CPx connected tothe floating diffusion 6 directly contacts the diffusion layer 60 as thefloating diffusion 6.

When the gettering layer is removed by etching, the front surface of thesemiconductor substrate 150 may be overetched. In this case, the surfaceof the diffusion layer 60 as the floating diffusion on the front side ofthe semiconductor substrate 150 is set back to the back side of thesemiconductor substrate 150 as compared with the surface of the impuritysemiconductor layer 10 of the photodiode 1 and the front surface shieldlayer 18 on the front side of the semiconductor substrate 150.

For example, the metal impurity region in the diffusion layer 60 may beremoved together with the gettering layer.

When the gettering layer is removed, the mask layer that selectivelyexposes the gettering layer is formed on the semiconductor substrate 150after gettering substantially, for example, in the same manner as inFIG. 10.

In accordance with the mask layer formed on the semiconductor substrate150, the gettering layer is selectively removed by etching (e.g., RIE).

Thus, the image sensor according to the present embodiment having thestructure shown in FIG. 11 is formed.

As in the example shown in FIG. 11, the gettering layer (the metalimpurity region) is completely removed after the gettering treatment,and it is thereby possible to prevent the metal impurity in thegettering layer from diffusing into the semiconductor substrate 150.

EXAMPLE 3

The modification of the image sensor and the manufacturing method of thesame according to the embodiment are described with reference to FIG. 12and FIG. 13.

FIG. 12 is a sectional view illustrating the modification of the imagesensor according to the embodiment.

As shown in FIG. 12, a silicide layer 67 may be provided on a getteringlayer 61.

The silicide layer 67 on the gettering layer 61 is formed by thesilicide treatment of the gettering layer 61. For example, when thegettering layer 61 is a layer including P, Ge, or B, the silicide layer67 may including the impurity in the gettering layer 61 in addition tothe silicon element and the metal element (e.g., nickel or cobalt) thatincludes silicide together with the silicon element.

For example, silicide layers 27 and 37 are provided on the gateelectrodes 20 and 30 of the transistors 2 and 3.

The process of forming the silicide layer 67 on the gettering layer 61is described with reference to FIG. 13. FIG. 13 is a sectional processview illustrating the modification of the image sensor manufacturingmethod according to the embodiment.

For example, the silicide treatment of the gettering layer issimultaneous with the silicide treatment of the gate electrodes and thesource/drain diffusion layers of the transistors in the pixel array andin the peripheral circuit region.

After an insulating layer 201 is deposited on the semiconductorsubstrate 150, the insulating layer covering the region in which thesilicide layer is formed is selectively removed by lithography and RIE.The gate electrodes 20 and 30 of the transistors 2 and 3 and thesource/drain regions are exposed. On the other hand, the upper surfaceof the impurity semiconductor layer 10 of the photodiode 1 is covered bythe insulating layer 201. At the same time, the insulating layer 201covering the gettering layers 61 and 65 is removed, and the getteringlayers 61 and 65 are exposed.

A metal film 202 for forming the silicide layer is formed on the gateelectrodes 20 and 30, on the source/drain diffusion layer, on thegettering layers 61 and 65, and on the insulating layers 201 and 29.

After the metal film 202 is deposited, the semiconductor substrate 150is subjected to a heat treatment. Silicon included in the gateelectrodes 20 and 30, the source/drain diffusion layer 35, and thegettering layers 61 and 65 reacts (hereinafter referred to as a silicidereaction) with the elements that form the metal film 202.

Thus, as shown in FIG. 12, the silicide layers 27, 37, and 67 are formedin a self-aligning manner in a contact portion between the gateelectrodes 20 and 30 and the metal film 202, a contact portion betweenthe source/drain diffusion layer 35 and the metal film 202, and acontact portion between the gettering layers 61 and 65 and the metalfilm 202. The silicon layer covered by the insulating layers 201 and 29does not directly contact the metal film 202, and is therefore notsilicided.

After the silicide layers 27, 37, and 67 are formed, the metal filmwhich has not reacted with silicon is selectively removed.

The interlayer insulating film, the contact plug, and the interconnectare then sequentially formed as described above, and the image sensoraccording to the embodiment is formed. The contact plugs CPx and CPz areconnected to the silicide layer 67 on the gettering layers 61 and 65.

As long as the silicide layer is formed after gettering, the getteringlayers 61 and 65 may be entirely silicided.

As the silicide layer 67 is provided on the gettering layer 61, thecontact resistance between the contact plugs CPx and CPz and the layer61 which functions as the floating diffusion can be reduced.

The silicide layer 67 (or the gettering layer made of silicide) isformed on the gettering layer 61 by substantially the same process asthe process of forming the silicide layer on the gate electrode of thetransistor and the source/drain diffusion layer. Therefore, the numberof manufacturing processes of the image sensor is not increased by theprocess of forming the silicide layer 67 on the gettering layers 61 and65.

Thus, according to the image sensor shown in FIG. 13, the electriccharacteristics of the image sensor can be improved without the increasein number of manufacturing processes of the image sensor.

As described above, the advantageous effects substantially similar tothose according to the first embodiment can also be obtained in themodifications shown in FIG. 10 to FIG. 13.

(3) Application Example

An application example of the solid-state image sensing device accordingto each embodiment is described with reference to FIG. 14.

The solid-state image sensing device (image sensor) according to theembodiment is formed into a module, and applied to a digital camera or acamera-equipped mobile telephone.

FIG. 14 is a block diagram showing the application example of the imagesensor according to the embodiment.

A camera (or camera-equipped mobile telephone) 900 including the imagesensor 100 according to the present embodiment includes, in addition tothe image sensor 100, for example, an optical lens unit 101, a signalprocessing unit (e.g., digital signal processor (DSP)) 102, a storageunit (memory) 103, a display unit (display) 104, and a control unit(controller) 105.

The image sensor 100 converts light from a subject into an electricsignal.

The lens unit 101 collects the light from the subject to the imagesensor 100, and forms a figure corresponding to the light from thesubject into an image on the image sensor 100. The lens unit 101includes a plurality of lenses and optical characteristics (for example,the focal length) of the lens unit 101 can mechanically or electricallybe controlled by a combination of each lens.

The DSP 102 processes the signal output from the image sensor 100. TheDSP 102 forms an image (image data) corresponding to a subject based ona signal from the image sensor 100.

Image data from the DSP 102 is stored in the memory 103. Externallysupplied signals and data, and signals and data directly supplied fromthe image sensor 100 can also be stored in the memory 103. The memory103 may be a memory chip such as a DRAM or flash memory loaded in thecamera 900, or may be a memory card or a USB memory removable from thebody of the camera 900.

The display 104 displays the image data from the DSP 102 or the memory103. The data from the DSP 102 or the memory 103 is still image data ormoving image data, and still images or moving images are displayed onthe display 104.

The controller 105 controls the operations of the components 100 to 104in the camera 900.

As described above, the image sensor 100 according to the presentembodiment can be applied to the camera 900.

The camera 900 including the image sensor 100 according to the presentembodiment can improve the quality of an image to be formed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A solid-state image sensing device comprising: aphotoelectric converting element which is provided in a semiconductorsubstrate and which converts incident light to a charge; a floatingdiffusion which is provided in the semiconductor substrate and to whichthe charge is transferred; and a read transistor which is providedbetween the floating diffusion and the photoelectric converting elementin the semiconductor substrate and which controls the transfer of thecharge, wherein the floating diffusion includes a metal impurity, thefloating diffusion includes a diffusion layer provided in thesemiconductor substrate, a first semiconductor layer which is providedon the diffusion layer and which includes a first impurity, and animpurity region which is provided in the diffusion layer and whichincludes the metal impurity, the impurity region abutting on the bottomof the first semiconductor layer, the concentration of the metalimpurity in the floating diffusion is higher than the concentration of ametal impurity in the photoelectric converting element, and theconcentration of the metal impurity in the impurity region is equal toor less than the concentration of the metal impurity in the firstsemiconductor layer and is equal to or more than the concentration ofthe metal impurity in the diffusion layer.
 2. The solid-state imagesensing device according to claim 1, wherein a concentration of themetal impurity in the first semiconductor layer is higher than aconcentration of the metal impurity in the diffusion layer.
 3. Thesolid-state image sensing device according to claim 1, wherein thefloating diffusion includes a silicide layer provided on the firstsemiconductor layer, and a contact portion is connected to the silicidelayer.
 4. The solid-state image sensing device according to claim 1,further comprising: a transistor which is provided in a firstsemiconductor region within the semiconductor substrate and whichincludes a gate electrode, a source/drain diffusion layer, and a secondsemiconductor layer on the source/drain diffusion layer, wherein thesecond semiconductor layer includes the same material as the firstsemiconductor layer, and a concentration of a metal impurity in thesecond semiconductor layer is higher than the concentration of the metalimpurity in the photoelectric converting element.
 5. The solid-stateimage sensing device according to claim 1, wherein the firstsemiconductor layer includes a silicon layer including at least one ofphosphorus, germanium, and carbon as the first impurity, and the firstsemiconductor layer includes a gettering site by the first impurity.